High bulk coalescing filter media and use thereof

ABSTRACT

The present invention relates to a coalescence filter for purifying a fluid which contains a carrier and at least one liquid contaminant by coalescing of the at least one contaminant, wherein the coalescence filter includes an inlet for supplying the fluid to a filter element present in the coalescence filter, wherein the filter element includes a primary coalescence medium which is provided for coalescing of the at least one contaminant in the primary coalescence medium during the displacement of the fluid through the primary coalescence medium, wherein the coalescence filter further includes an outlet for discharging the coalesced contaminant from the filter element, wherein the primary coalescence medium comprises at least one layer of a porous material, wherein the primary coalescence medium has a total thickness of at least 3.5 mm.

This invention relates to a coalescence filter for purifying a fluidwhich contains a carrier and at least one liquid contaminant bycoalescing of the at least one contaminant, wherein the coalescencefilter includes an inlet for supplying the fluid to a filter elementpresent in the coalescence filter, wherein the filter element includes aprimary coalescence medium which is provided for coalescing of the atleast one contaminant in the primary coalescence medium during thedisplacement of the fluid through the primary coalescence medium,wherein the coalescence filter further includes an outlet fordischarging the coalesced contaminant from the filter element, whereinthe primary coalescence medium comprises at least one layer of a porousmaterial, according to the pre-characterizing part of the first claim.

The use of coalescence filters for coalescing a dispersed phase from amixture of two immiscible phases, a continuous and a dispersed phase, isknown per se. Examples of practical applications include separating oilaerosol droplets from compressed air coming from air compressors andcrankcases, separating water as a dispersed phase from fuel as acontinuous phase in fuel-water systems, or separating oil as a dispersedphase from a water-oil system with water as a continuous phase.

Coalescence is induced by a coalescence medium, which typicallycomprises a plurality of layers of one or more porous, fibroussubstrates, which may be wettable (oleophilic or fluid-attracting oradsorbent) or non-wettable (oleophobic or fluid-repellent). The fibrousmaterial has a surface that induces aggregation or coalescence of thedispersed phase. A disperse fluid with droplets of a dispersed phase ismoved by the continuous phase or carrier of the fluid through thecoalescence medium, for example, oil-contaminated air. The dispersedphase often coalesces already in the first layers on the fibers of thecoalescence medium. Upon continuous supply of fluid, the droplets growinto larger drops. The drops are transported with the air flow throughthe filter, and as soon as they reach a size that does not adhere to thefibers of the coalescence medium anymore, they exit the filter,typically under the influence of gravitation. After being in use forsome time, the filter usually reaches a steady state condition, wherethe rate of accumulation of the dispersed phase of fluid drops in thecoalescence medium corresponds to the rate of drainage from the filter.Coalesced drops typically have a drop diameter of 5 to 500 μm.

For manufacturing coalescence filters, diverse kinds of materials areused, for instance, organic and inorganic fibrous or porous materials.These materials are available in diverse forms, for instance, ashomogeneous, heterogeneous, layered or pleated or rolled materials,composites, laminates and combinations thereof. Forms suitable for useas coalescence filter are typically a web, cloth, cylinder, cube orother simple or complex geometric shape. The separating capacity of afilter material depends on numerous parameters including the compositionand orientation of the fibers in the filter or coalescence medium, theyield of the filter material under the practical conditions, theconcentration of the contaminants (dispersed phase) in the carrier(continuous phase), the pressure to which the filter material issubjected, and the volume of continuous phase to which the filter isexposed over time.

Numerous attempts were undertaken to improve the separating power of acoalescence filter unit, inter alia by the use of complex fiberstructures or porous structures in the coalescence medium.

U.S. Pat. No. 8,114,183 describes a coalescence filter for separating animmiscible continuous and dispersed phase. The coalescence filterincludes an axially extending coalescence element with a coalescencemedium comprising a plurality of fibers oriented in gravitationaldirection. As a result of the fibers of the coalescence medium extendingtangentially along the perimeter of the coalescence element, the flowresistance is reduced and drainage to the exit at the bottom ispromoted. The coalescence element has a cross section in a directiontransverse to its axis in the form of a closed loop with an innercavity. To realize a highest possible drainage pressure, the verticaldimension is as great as possible and the transverse dimensions of thecoalescence element decrease towards the bottom. U.S. Pat. No. 8,114,183further describes having the average fiber diameter and/or the porosityof the coalescence element decrease towards the center of thecoalescence element, with a view to capturing contaminants of largerdimensions, which may cause occlusion of the coalescence element, in theinitial, open, less restrictive layers.

From U.S. Pat. No. 8,409,448 it is known for a coalescence filter forremoving an immiscible lipophilic or hydrophilic liquid, respectively,from a continuous hydrophilic or lipophilic liquid phase, respectively,to be built up from a blend of fibers having varying hydrophobic andhydrophilic surface properties. Coalescence and wetting can becontrolled by controlling the amount of hydrophobic and hydrophilicfibers.

The prior art coalescence filters, however, exhibit the disadvantagethat the pressure drop across the filter is often still too great, inother words, that a great pressure decrease occurs across the filter,which adversely affects the filter performance. A known measure forreducing the pressure drop is to take away or reduce the number oflayers of filter material. This, however, has an adverse effect on thefilter efficiency. Filter efficiency refers to the amount of fluid thatis filtered by the coalescence filter relative to the amount of fluid atthe inlet of the filter. There is thus a need for a coalescence filterthat exhibits a highest possible filter efficiency in use.

This invention therefore contemplates the provision of a coalescencefilter having an improved filter efficiency.

This is achieved according to the invention with a coalescence filterthat has the technical features of the characterizing part of the firstclaim.

Accordingly, the coalescence filter of this invention is characterizedin that the primary coalescence medium has a total thickness of at least3.5 mm, preferably at least 4 mm, preferably at least 5 mm, morepreferably at least 6 mm, most preferably at least 7 mm, in particularat least 7.5 mm, measured in the flow direction of the fluid to becoalesced, at a pressure of 2N/cm². Within the purview of thisinvention, “total thickness” is understood to mean that the thickness ofthe primary coalescence medium is measured in the direction in which thefluid flows through the coalescence filter and hence the coalescencemedium, while the primary coalescence medium is subjected to an ambientpressure of 2N/cm².

The great layer thickness of the primary coalescence medium according tothis invention in comparison with the prior art coalescence filtersmakes it possible to improve the filter efficiency. The great layerthickness enables in particular a considerable increase of thecoalescence yield, i.e., the amount of contaminant that is filtered bythe primary coalescence medium or is coalesced in the primarycoalescence medium, relative to the amount of contaminant at the inletof the filter.

The inventors have found in addition that in the coalescence medium ofthis invention, the capillary pressure is hardly influenced by thegreater layer thickness of the primary coalescence medium, and that alsothe resistance to be overcome by the fluid during its displacementthrough the primary coalescence medium (the so-called channel pressure)remains limited and is small compared to the capillary pressure. This issurprising since it is customary in the prior art, for the purpose ofincreasing filter efficiency, to limit or lower the layer thickness ofthe coalescence filter, for instance by using a limited number of layersof porous material, in order to keep the pressure drop across the filterlow. This invention now makes it possible not only to improve the filterefficiency, but also to reduce the pressure drop across the coalescencefilter, and thus to improve filter performance.

For the purpose of practical usefulness in existing filter devices andin view of costs, the primary coalescence medium preferably has a totalthickness of 50 mm at a maximum, preferably 40 mm at a maximum, morepreferably 30 mm at a maximum, most preferably 25 mm at a maximum, inparticular 20 mm at a maximum. In fact, the inventors have found thatthe filter efficiency is not significantly improved at a greaterthickness of the primary coalescence medium and that the material costtends to become disproportionately high then. With increasing thickness,moreover, there is a risk that the pressure to be overcome by thecoalesced contaminant to move through the primary coalescence medium,the so-called channel pressure, becomes too high. In fact, the inventorshave found that once coalescence of the contaminant into larger dropshas occurred, transport through the primary coalescence medium takesplace under the influence of the transport of the carrier present in thefluid through the coalescence medium. It appeared then that the pressureto be overcome to transport the coalesced drops through the primarycoalescence medium, in the form of channels extending throughout thethickness of the coalescence medium, depends on the thickness of theprimary coalescence medium.

The primary coalescence medium of this invention can be simplymanufactured, for instance, by processing a fibrous material, forinstance glass fibers, in such a way that a layer-form or sheet-formmaterial is provided having pores or openings between the fibers. Thepores in the fibrous material of the coalescence medium through whichthe fluid moves and in which coalescence takes place are substantiallyformed by the spaces that are present between the fibers of the fibrousmaterial. Suitable techniques that make this possible are known to theskilled person and comprise inter alia manufacturing one or more sheets,for instance, woven or nonwoven fibrous materials, knitted materials,braided fibers, films, scrims, and combinations of the aforementionedmaterials or laminates or composites thereof. Fibrous materials suitablefor use in a primary coalescence medium of this invention are known tothe skilled person, and are preferably so chosen as to be able to effectthe capture and coalescence of the contaminant in the coalescencemedium. However, other porous materials may also be suitably used asprimary coalescence medium.

The primary coalescence medium is preferably a porous material havingpores of an average diameter of between 2 and 100 μm, preferably between3 and 70 μm, more preferably between 5 and 50 μm, in particular between5 and 35 μm, more particularly between 5 and 30 μm.

A primary coalescence medium whose porosity is provided by pores asdescribed above, has an open structure.

A primary coalescence medium manufactured from a fibrous material willmostly substantially contain fibers having an average diameter of0.25-20 μm, preferably 0.5-10 μm, although fibers of a still smaller orgreater diameter may be present. Mostly, the primary coalescence mediumwill be made up of a multiplicity of fibers whose diameter varies withinthe aforementioned limits.

The primary coalescence medium of this invention preferably has an airpermeability of at least 30 l/m².s, preferably at least 50 l/m².s, morepreferably at least 60 l/m².s, most preferably at least 80 l/m².s, inparticular at least 100 l/m².s or more. The air permeability can varywithin wide limits and in practice will typically not be higher than2,000 l/m².s, preferably 1,750 l/m².s at a maximum. The air permeabilityis measured at 2 mbar according to DIN EN ISO 9237.

A primary coalescence medium with such an air permeability has an openstructure.

According to the invention, it is thus possible to obtain a primarycoalescence medium having an improved performance, which is able toprovide a better separation yield of the contaminant present in thefluid, by making use of a primary coalescence medium having a greatertotal thickness in combination with a more open structure, than knownheretofore.

The open structure contributes to enabling a considerable increase ofthe coalescence yield, i.e., the amount of contaminant that is filteredby the primary coalescence medium or is coalesced in the primarycoalescence medium, relative to the amount of contaminant at the inletof the filter. This is in contrast to the prior art, which teaches, forthe purpose of increasing filter efficiency, the use of a primarycoalescence medium of a lesser thickness, in which the pores have asmaller mean diameter.

The inventors have further found that in the use of a primarycoalescence medium with an open structure as described above, also thecapillary pressure to be overcome by a coalescing fluid upon flowinginto the pores of a non-wetting primary coalescence medium (forinstance, an oil repellent or oleophilic coalescence medium) can bereduced considerably, as well as the capillary pressure to be overcomeby the coalesced liquid upon exiting a wetting primary coalescencemedium (for instance, an oil adsorbing or oleophilic coalescencemedium). This lower capillary pressure provides the advantage that theprimary coalescence medium can have a much greater thickness and a moreopen structure than was considered possible heretofore, so that thecoalescence yield can be raised considerably, and that nonetheless thepressure drop across the coalescence filter can be kept sufficientlylow. The thickness is measured in the flow direction of the fluid to becoalesced. In practice, this can mean that the primary coalescencemedium can be made up of a much greater number of layers of filtermaterial than was customary hitherto, and that at the same time thepressure drop across the coalescence filter can be kept sufficientlylow.

The inventors have actually established that in the use of a primarycoalescence medium having smaller pores and hence a more closedstructure, the pressure drop across the coalescence medium proves to beconsiderably higher. Consequently, in the use of a coalescence mediumhaving smaller pores, it is necessary to keep the thickness low toensure a sufficiently low pressure drop across the coalescence filter.

A reduced capillary pressure further provides the advantage that theenergy needed for supplying a contaminant into the pore system of anon-wetting primary coalescence medium can be reduced, as well as thecapillary pressure to be overcome upon a contaminant exiting a wettingprimary coalescence medium. A non-wetting primary coalescence medium isunderstood to mean that the coalescence medium exhibits a low affinityfor the coalescing liquid, or, in other words, that substantiallyrepulsive forces occur between the two materials. Examples of anon-wetting primary coalescence medium include an oleophobic and/orhydrophobic primary coalescence medium. A wetting primary coalescencemedium is understood to mean that the primary coalescence mediumexhibits a high affinity for the coalescing liquid or, in other words,that substantial forces of attraction occur between the primarycoalescence medium and the coalescing liquid. Examples of a wettingprimary coalescence medium include an oleophilic and/or hydrophilicprimary coalescence medium.

The skilled person is able to tailor the thickness of the primarycoalescence medium, taking into account the nature of the primarycoalescence medium, particularly taking into account the mean size ofthe pores of the coalescence medium and/or the air permeability and/ordensity of the coalescence medium, so as to enable the intendedperformance.

The primary coalescence medium may be made up of a plurality of closelystacked or closely wrapped adjacent layers of a sheet-form porous filtermaterial, although the use of a single layer having a desired thicknessis also possible. Closely stacked is understood to mean that successivelayers are in contact with each other or, in other words, thatsuccessive layers are arranged adjacently. Adjacent layers of sheet-formcoalescence medium are preferably stacked such, or a sheet of thecoalescence medium is wrapped such, that successive layers of thecoalescence medium are arranged adjacently, that the distance betweensuccessive layers is minimal, and that any layer of air present betweensuccessive layers has a minimal thickness or, preferably, is evenabsent. This makes it possible for the capillary pressure that is to beovercome upon transition of the fluid from one layer to the other, to bekept as low as possible. This also makes it possible to minimize therisk of the fluid flowing out between successive layers.

In an embodiment, successive layers of the primary coalescence mediummay be made up of a same porous material. By stacking layers of the samematerial, it is possible to prevent an additional capillary pressureneeding to be overcome when the fluid from a previous layer enters anext layer, and it is consequently possible to minimize the risk ofincrease of the pressure drop across the coalescence filter as a resultof material transitions. In another embodiment, two or more successivelayers of the primary coalescence medium are made up of differentmaterials, in particular, materials having a different average porosityand/or a different average pore diameter and/or a different densityand/or a different air permeability. It is also possible to build up theprimary coalescence medium from a first primary coalescence medium and asecond primary coalescence medium, the first primary coalescence mediumbeing made up of one or more layers of a first material, for instance awetting, oleophilic or hydrophilic coalescence medium, and the secondcoalescence medium being made up of one or more layers of a secondmaterial, for instance, a non-wetting, oleophobic or hydrophobiccoalescence medium.

In case the primary coalescence medium is made up of a plurality oflayers, the layer thickness of the individual layers may vary withinwide limits. The layer thickness of the individual layers of the primarycoalescence medium may vary, for instance, from 0.1 to 1 mm, preferably0.4 mm, more preferably 0.5 mm, most preferably 0.6 mm. The skilledperson is able to select the desired layer thickness taking into accountthe total layer thickness intended for the coalescence medium.

The primary coalescence medium of this invention includes preferably atleast 4 successive layers of a same porous material to guarantee asufficient degree of coalescence, more preferably at least 6 layers,most preferably at least 10 layers. The number of layers will generallynot be more than 30, since the filter efficiency is not significantlyimproved if the primary coalescence medium includes more layers, and thematerial cost then tends to become disproportionally high. A furtherincrease of the number of layers moreover entails a risk of the channelpressure becoming too high, as has been explained hereinabove.Preferably, the number of layers of material from which the primarycoalescence medium is built up is not more than 25, most preferably notmore than 20.

The inventors have further found that during fluid flow through amultilayer primary coalescence medium as described above, thecontaminant present in the fluid coalesces in the pores or openingspresent in the primary coalescence medium. The pores of successivelayers seem to form quasi-continuous channels extending in the flowdirection of the fluid, through the coalescence medium, and providepreferred pathways along which the fluid moves.

Without wishing to be bound by this theory, the inventors believe thatthe pores of successive material layers which the primary coalescencemedium is comprised of, overlap at least partly, so that pores from aprevious layer link up at least partly with, and in that way provideaccess to, pores in a next layer. Thus, a kind of channels or preferredpathways are formed which extend through several layers of the primarycoalescence medium, through which the fluid moves. Preferred pathways insuccessive layers will mostly not be perfectly congruent. Rather,preferred pathways will partly, to a greater or lesser extent, butsometimes also wholly, link up with each other, and in that way formquasi-continuous channels in which the contaminant can deposit. Thesequasi-continuous channels extend throughout the thickness of thematerial of the primary coalescence medium, in the flow direction of thefluid. The inventors further believe that these quasi-continuouschannels in the primary coalescence medium exhibit a higher permeabilityto the fluid than the surrounding material does, or, in other words,form channels having a higher flow capacity for the fluid.

The inventors have further found that the above-describedquasi-continuous channels in successive layers are located in theprimary coalescence medium in each other's proximity, laterally. Withoutwishing to be bound by this theory, the inventors believe that acontaminant present in a layer of the coalescence medium spreadslaterally to some extent and locally forms a spot or, in other words, alocal continuous phase. Supposedly, the contaminant moves alongpreferred pathways where the least resistance is to be overcome. Thus,the coalesced contaminant forms a continuous phase, which extends bothlaterally in the coalescence medium and in the depth or flow directionof the fluid. The afore-described process repeats itself in thethickness direction and/or in successive layers of the primarycoalescence medium.

The assumption that preferred pathways are present in the layeredstructure of the coalescence medium of this invention is plausible.Porous filter materials, in particular sheet-form filter materials madeup of fibrous materials, even if carefully manufactured, exhibit areasthat on a microscale are not homogeneous and exhibit a locally varyingpermeability with openings between the fibers. Air or any other fluidwill preferentially move though areas of higher/better permeability. Inthese areas of better permeability, a contaminant will first precipitatein the pores and coalesce into larger drops. These drops are moved withthe air flow through areas of better permeability. As a result of thehigh permeability areas in successive layers aligning with each other atleast partly, quasi-continuous channels form.

Within the purview of this invention, consequently, “channels” isunderstood to refer to the use of a preferred pathway by an amount ofcoalescing liquid periodically moved through the primary coalescencemedium under the influence of the flow of the fluid, for instance air.These pathways have a random shape and can extend in all directions.According to the invention, “channels” does not necessarily refer tocylinder-shaped tubes or conduits. With non-wetting coalescence mediathese channels give rise to the formation of drops at the exit of thefilter; with wetting coalescence media these channels spread in the lastlayer into a film, which has to be pushed out of the primary coalescencemedium under the influence of capillary force and thus leads tocapillary pressure drop.

In a preferred embodiment of this invention, the primary coalescencemedium has a density in the range of from 0.05 to 0.90 g/cm³, preferablyfrom 0.05 to 0.75 g/cm³, more preferably from 0.08 to 0.50 g/cm³. Thedensity is measured by weighing an amount of material of the primarycoalescence medium having an area of 1 m², and multiplying this by thethickness of this material, measured with a digital micrometer at apressure of 2N/cm².

The coalescence filter of this invention preferably includes, adjacentto a surface of the primary coalescence medium, a drainage layer,preferably along a downstream surface of the primary coalescence mediumalong which coalesced contaminant exits the primary coalescence medium,for taking up and draining coalesced contaminant and promoting thedischarge thereof. This drainage layer positioned downstream is alsointended to provide a barrier to resist reflux of coalesced contaminantback to the coalescence medium and/or, in particular, to the carrierpresent in the fluid. Without wishing to be bound by this hypothesis, itis supposed that the drainage layer forms a boundary or transitionalzone along the boundary surface of the primary coalescence medium alongwhich draining occurs, so that build-up of contaminant at the boundarysurface is counteracted, by formation of large drops which are driven bythe motive force of gravitation and are deposited in the housing of thefilter for discharge from the filter. Also, if desired, upstream of theprimary coalescence medium a protective layer may be arranged, adjacentto a surface of the primary coalescence medium along which fluid issupplied to the primary coalescence medium, in a manner such that thetwo materials are in contact. Downstream, also a protective layer may beadded, adjacent to a surface of the primary coalescence medium, which,in addition to a protective action, can also have an extra drainagefunction.

The invention also relates to a coalescence medium as described above aspart of and/or for use in a coalescence filter as described above.

The invention further relates to a method for purifying a fluid whichcontains a carrier and at least one contaminant, wherein the fluid isconducted through a coalescence filter as described above, for reducingthe concentration of the at least one contaminant by coalescing the atleast one contaminant in the coalescence filter, in particular in theprimary coalescence medium. The fluid may then be chosen, for instance,from the group of compressed air contaminated with one or morehydrocarbons, contaminated water or contaminated hydrocarbons, but otherfluids can likewise be suitably used. The coalescence filter of thisinvention is suitable for use in a continuous process in which acontinuous supply of fluid to the primary coalescence medium takesplace. It is also possible, however, to supply the fluid in one or morediscrete batches.

The invention furthermore relates to the use of the coalescence filterdescribed in this patent application for separating one or more liquidcontaminants from a carrier, wherein the carrier can be a gas or aliquid. The invention relates in particular to the use of thecoalescence filter described in this patent application for separatingoil aerosol drops from compressed air coming from air compressors andcrankcases, separating water as a dispersed phase from fuel as acontinuous phase in fuel-water systems, or separating oil as a dispersedphase from a water-oil system with water as a continuous phase.

The invention is further elucidated below in the appended figures andthe description of these figures.

FIG. 1 shows a view of the inner volume of a representative coalescencefilter for compressed gas.

FIG. 2a is a schematic cross section of a primary coalescence medium,relative to a drainage layer, with a carrier fluid (CF) being suppliedat an angle of 90° and the coalescence medium and the drainage layerarranged adjacently.

FIG. 2b is a schematic representation of a primary coalescence medium,relative to a drainage layer, with a carrier fluid (CF) being suppliedat an angle of between 1° and 90° and the coalescence medium and thedrainage layer arranged adjacently.

FIG. 3 shows a cross section of a quasi-continuous channel formed in theprimary coalescence medium, as is shown by a higher concentration ofdeposited liquid.

FIG. 4 shows an isometric view of a plurality of quasi-continuouschannels formed in the primary coalescence medium, as is shown byregional areas exhibiting a higher concentration of deposited liquid.

FIG. 5 is a graphic representation of the pressure drop of a carrierfluid through a coalescence medium including wetting (oleophilic) fibersaccording to this invention, given a carrier fluid flow with depositionof a liquid, oil-containing contaminant, as a function of time

FIG. 6 is a graphic representation of the pressure drop of a carrierfluid through a coalescence medium including oleophobic fibers accordingto this invention, given a carrier fluid flow with deposition of aliquid contaminant, as a function of time

The coalescence filter 10 shown in FIG. 1 includes a closed housing 24with a filter head 12 at the top. Filter head 12 includes an inlet 16via which a fluid containing a carrier liquid and at least onecontaminant is introduced into the coalescence filter. The housing 24includes an outlet 18 for discharging a fluid and/or carrier liquidwhich has flowed through the filter element. Filter head 12 isdetachably connected with housing 24, so that the inner space of thecoalescence filter is accessible for replacement of the filter elementif necessary. The detachable connection can be effected in any mannerconsidered suitable by the skilled person, for instance, by means of athreaded connection, by means of pressure, friction, clamping, etc.Inlet 16 is connected with a filter element in such a manner that afluid can be passed to the filter element. The filter element ispreferably detachably connected with the filter head 12, so that thefilter element can be replaced periodically, or can be replaced ifnecessary.

The coalescence filter shown in FIG. 1 is intended for coalescing one ormore liquid contaminants present in a liquid or gaseous carrier of afluid. The one or more contaminants can be, for instance, an inert orreactive substance. The one or more contaminants may, for instance,belong to the group of liquids, aerosols, macrodrops or mixtures of twoor more of these materials. An example of a fluid suitable for use withthe coalescence filter of this invention is compressed air, contaminatedwith an oil aerosol.

The filter element includes at least one primary coalescence medium 22,for coalescing in the coalescence medium one or more liquid contaminantspresent in the fluid and separating these contaminants from a carrierpresent in the fluid. Depending on the intended application, especiallyif coalescence of a plurality of contaminants is intended, it may bechosen to install two or more different primary coalescence media, eachwith a desired affinity for the contaminant to be removed.

In a preferred embodiment, the filter element additionally includes,adjacent to the coalescence medium 22 and downstream from thecoalescence medium 22, at least one porous drainage layer 30. Thisdrainage layer is positioned adjacent to a surface of the coalescencemedium, with or without a layer of air or other physical separationbetween the two media, preferably without a layer of air. Purpose is toenable an energy-efficient flow of fluid, carrier and/or contaminantfrom the coalescence medium to the drainage layer. This is shown inFIGS. 2a and 2b . The drainage layer is mostly arranged downstream ofthe primary coalescence medium.

A drainage layer 30 positioned downstream is intended to maximize thetransfer and delivery/discharge of the contaminant separated from thefluid by the primary coalescence medium due to the motive force of thefluid and/or the carrier present therein which is conveyed through thefilter, on the one hand. Materials that enable this are known to theskilled person. The material of the drainage layer 30 preferably alsoprovides a barrier to resist reflux of the coalesced contaminant back tothe primary coalescence medium 22 but, in particular, to the carrier.Without wishing to be bound by this, it is supposed that the drainagelayer 30 provides a boundary or transitional zone for the adjacentsurface of the coalescence medium 22, which counteracts any build-up ofcoalesced contaminant on this contact surface in that it stimulates theformation of macroscopic drops of the contaminant liquid. These dropsare thereupon driven off the drainage layer 30 by an additional motiveforce, such as gravity, and, for instance, deposited or precipitated inthe housing and discharged from the filter. If desired, two or moredrainage layers 30 may be provided. An example of a suitable material isan open cell polymeric foam.

If desired, upstream but also downstream of the primary coalescencemedium 22, a protective layer 25 may be provided. This protective layer25 can also serve as a drainage layer, or direct the fluid flow in adesired direction. An example of a suitable material for use as aprotective layer 25 is an open polypropylene layer, but other materialscan also be used. Preferably, the filter element also includes a core20. The at least one primary coalescence medium 22 is arrangeddownstream of the filter core 20.

The coalescence filter 10 preferably includes one or more internalsupport structures 26, which support integration of the filter elementinto one mechanical whole, which minimize the risk of mechanicaldeformation of the filter materials including the coalescence medium 22,under the influence of loading by the fluid, and protect same againstthe action of unexpected or momentary impact.

The housing 24 may further include a drainage mechanism 32. A suitabledrainage mechanism 32 can include automatically, semiautomatically ormanually operated valves, via which a coalesced and drained contaminantretained in the housing is removed.

The coalescence filter 10 can further include optional components, whichfurther improve the use and the yield of the filter. Filter head 12 caninclude, for instance, a status indicator 14, which gives an indicationabout the status of the coalescence filter, including the potentialnecessity for a periodic replacement. The status indicator 14 may beprovided for directly or indirectly measuring the yield of thecoalescence filter and may include an indicator providing indicia of thecondition of the coalescence filter 10, by means of, for instance, avisual, auditory or electronic signal or a combination thereof. Theindicator 14 may work pneumatically or electrically or according to anyprinciple considered suitable by the skilled person.

The primary coalescence medium 22 used in the coalescence filter of thisinvention has a porous structure, which can induce aggregation orcoalescence of one or more contaminants present in the fluid. Thesurface of the pores present in the porous structure of the primarycoalescence medium may be wetting with respect to one or more of thecontaminants to be coalesced, or non-wetting. The surface may be, forinstance, oleophobic or hydrophobic, or oleophilic or hydrophilic. Inapplications where removal of oil from a liquid or gas stream isintended, the coalescence medium can be oleophilic or oleophobic. Thematerial for the primary coalescence medium 22 is preferably so chosenas to have a high affinity for the impurity to be removed.

To make it possible for contaminants of a various nature to be removedin succession, the coalescence filter of this invention can include twoor more primary coalescence media 22 of different affinity selective forthe contaminant to be removed. Preferably, however, to keep thecapillary pressure as low as possible, the coalescence filter includesjust one primary coalescence medium.

The primary coalescence medium is a porous material which can includeone or more layers of a porous material, and is preferably layered. Theprimary coalescence medium is preferably made up of one or more layersof a same layer-form fibrous material. In an alternative embodiment, thecoalescence filter includes two or more filter elements with differentcoalescence media, i.e., a plurality of coalescence media of differentaffinity selective for the contaminant to be removed.

Suitable layer-form materials for use as primary coalescence medium 22comprise substrates or materials comprised of finite length fibers,continuous filaments and combinations thereof. The primary coalescencemedium preferably includes suitable materials which are resistant to thepressure applied to enable displacement of the fluid through the primarycoalescence medium, to the liquid contaminants present in the fluid, andto the static and dynamic loads to which the material is exposed duringthe manufacture of the filter, assembly thereof, and use thereof.Examples of suitable layer-form fibrous materials include woven ornonwoven fibrous materials, knitted materials, plaiting, films, andcombinations of these materials or laminates or composites thereof.

The primary coalescence medium is preferably a multilayered material,which preferably includes at least 4 layers, more preferably at least 6layers, most preferably at least 10 layers. Mostly, the number of layersof fibrous material will not be higher than 20. The thickness of theindividual layers of the coalescence medium is not critical for thisinvention and may vary within wide limits. The thickness of a layer canbe, for instance, a thickness of 0.4 mm, 0.5 mm, 0 6 mm, 0.75 mm or 1mm. On the other hand, the primary coalescence medium may also be madeup of one layer of the desired material, in the desired thickness.

A multi-layered primary coalescence medium can be produced in differentways, for instance, by stacking, pleating, rolling or wrapping aplurality of layers of a fibrous material, so that the desired number oflayers is obtained. However, any other method can be suitably used. Thelayers of the fibrous material are preferably arranged adjacentlyrelative to each other, such that a layer of air of a least possiblelayer thickness is present between adjacent layers. Preferably, adjacentlayers are so arranged that no layer of air is present between them.This can be obtained, for instance, by pressing a plurality of stackedlayers together or clamping them, for instance along one or more sidesof the fibrous material. Preferably, however, the fibrous material iswrapped, to keep the risk of damage minimal.

Examples of fibrous materials that are particularly suitable formanufacturing a layered material for use in the primary coalescencemedium of this invention comprise thermoplastic materials, thermosettingmaterials, organic or inorganic materials, metallic materials or alloys,admixtures, blends and chemically modified materials, for instancemanufactured by drawing, spinning, needling, hydroentanglement, meltspinning (for instance, spin bonding, nanofibers, melt blowing),wet-laying, electro-spinning, solvent spinning, point bonding, adhesivebonding, continuous weave/knit, casting, co-extrusion, etc. Materials ofparticular preference comprise glass fibers, silicate-based wet-laidthermosetting adhesive bond nonwoven fabrics, for instance, aborosilicate glass fiber of finite length, because of their thermal andhydrothermal resistance to loading by the fluid, the carrier liquid andthe contaminant, without the need of chemical modification, for instanceby a fluorocarbon surface treatment.

Primary coalescence media suitable for use in this invention have adensity which preferably varies between 0.05-0.90 g/cm³, more preferably0.05-0.75 g/cm³, most preferably 0.08-0.50 g/cm³. Materials having adensity of between 0.10-0.25 g/cm³ or 0.12-0.17 g/cm³ can also besuitable and be preferred for well-defined fluids and/or contaminants.

The average diameter of the pores present in the material which theprimary coalescence medium is made up of (measured with microscopy) ispreferably in the range of 2 to 100 μm, preferably between 3 and 70 μm,more preferably between 5 and 50 μm, most preferably between 5 and 35μm, in particular between 5 and 30 μm.

Materials for use in the drainage layer 30 can be, for instance, wovenor nonwoven materials, knitted materials, films, open cell foams, castor spun scrims, open meshes and combinations of laminates or compositesof the aforementioned materials. Materials for use in the drainage layer30 may be chosen, for instance, from the group of thermoplastic orthermosetting plastics, organic or inorganic substances, metallicmaterials or alloys, blends of the aforementioned materials andchemically modified forms thereof. The aforementioned materials can bemanufactured in any manner considered suitable by the skilled person,for instance by drawing, spinning, needling, hydroentanglement, meltspinning (for instance, spin bonding, nanofibers, melt blowing),wet-laying, electro-spinning, solvent spinning, point bonding,through-air bonding, adhesive bonding, continuous weave/knit, casting,coextrusion, expansion, solvent cast and the like. Particularlypreferred are polyurethane foams, since they are well resistant tothermal loading by the fluid and/or the carrier and contaminant liquidpresent in the fluid, but at the same time counteract return of thecontaminants, for instance hydrocarbon-based contaminants, to thecoalescence medium, without the necessity of pretreating one or moreparts of the coalescence filter or the drainage layer withfluorine-containing substances.

The primary coalescence medium 22, the drainage layer 30 and the barrierlayer can be assembled in the coalescence filter 10 as separatelayer-form materials. It is also possible, however, to unite theaforementioned materials in a laminate, so that they form a whole, andoptimum contact between adjacent layers is ensured and optimum flow offluid from one layer to the next can take place.

This invention provides the advantage that the primary coalescencemedium is made up of one or more porous layered materials or structureshaving a high bulk volume and low density, with a large pore volume, thepores having a relatively great average pore diameter. Such an openstructure makes it possible to keep low both the capillary pressure andthe channel pressure in the transport of the fluid and the coalescedcontaminant through the primary coalescence medium and to keep thepressure drop across the coalescence filter low. Capillary pressure isunderstood to refer to the resistance that a contaminant must overcometo enter a non-wetting coalescence medium, but also the resistance thata contaminant must overcome upon exiting a wetting coalescence medium.Channel pressure is understood to refer to the resistance that acoalesced contaminant must overcome in its displacement through the poresystem of the coalescence medium.

The coalesced fractions of the liquid contaminant typically appear inthe coalescence medium as quasi-continuous channels with an increasedconcentration of coalesced liquid. These channels form discrete,perceptible areas which extend through the thickness of the filtermaterial as is shown in FIG. 4. The motive force of the carrier which isforcibly transported through the coalescence filter, for instance bypumping, takes care of the transport of the contaminants through thecoalescence medium towards the outlet or the rear, downstream outersurface of the primary coalescence medium, where the contaminants as aliquid fraction have reached a sufficient aggregation to leave thecarrier as macroscopic drops under the influence of gravity. It issupposed that the relatively large pores, the low density and high airpermeability of the primary coalescence medium of this inventioncooperate to enable a dynamic development of quasi-continuous channelsduring the useful life of the filter and to minimize the pressure dropacross the filter.

Without wishing to be bound by this theory, it is supposed that it ispossible that upon a first contact of a fluid, for instance compressedgas, with the primary coalescence medium 22, a first population ofdistinct quasi-continuous channels 50 is formed. As additional fluid issupplied, the accessibility of one or more of the quasi-continuouschannels 50 may lessen due to the formation of aggregates or immisciblecomplexes, gelling, and occlusion by solids and/or particles in thesechannels. Upon continued inflow of fluid, it is possible that aquasi-continuous channel 50 develops in a different direction of theprimary coalescence medium 22, along a pathway of lesser resistance.Thus, new quasi-continuous channels may form. Without wishing to bebound by this hypothetical model, it is supposed that upon transport ofa compressed flow of, for instance, air containing oil aerosol ascontaminant, through a primary coalescence medium, transport proceedsthrough one or more quasi-continuous channels 50. In these channels 50an effective reduction of the amount of oil in the air is brought aboutby coalescing of the oil in these channels 50.

FIG. 5 shows a practical situation for a coalescence medium made up ofan oleophilic fibrous structure. The inventors have established thatcoalescence of a liquid contaminant from the fluid proceeds according toa stepwise process, with at least a first and second discrete step, eachdiscrete step being associated with a decrease of the pressure acrossthe coalescence medium. A second discrete step was observed when thecontaminant leaves the coalescence medium and is associated with anenergy barrier which must be overcome upon leaving the coalescencemedium for overcoming a force of attraction. A first discrete step wasobserved upon the movement of the contaminant through the coalescencemedium in the form of one or more quasi-continuous channels in that theliquid must be pumped through the coalescence medium.

FIG. 6 shows a practical situation for a coalescence medium made up ofan oleophobic fibrous structure. The inventors have established thatcoalescence of the liquid contaminant from the fluid is accompanied by astepwise pressure decrease across the coalescence medium, with at leasta first and second discrete step. A first discrete step occurs upon thecontaminant flowing into the coalescence medium for overcoming therepulsive force. A second small discrete step occurs upon the transportof the contaminant through the coalescence medium through one or morequasi-continuous channels.

This invention thus provides a coalescence filter with a coalescencemedium comprising a plurality of layers of a fibrous material with poresof a relatively great average diameter, through which the fluid withcarrier and at least one contaminant move. The fibrous material has ahigh air permeability, a low density and contains a pore system whosepores have a relatively great diameter. This makes it possible toprovide a primary coalescence medium that ensures a higher separationyield of a contaminant present in the fluid. This higher separationyield is accompanied by a considerable reduction of the capillarypressure that is to be overcome by the fluid upon flowing into orexiting from the coalescence medium, but also by a considerable decreaseof the channel pressure, that is, the pressure to be overcome in thetransport of the fluid and the coalesced contaminant through the poresystem of the primary coalescence medium. As the pressure drop acrossthe coalescence medium can be reduced, the energy requirement of thefilter system can be improved considerably. This invention thus providesa coalescence filter having an improved separation yield in combinationwith a reduced energy requirement. This is surprising since in the priorart systems an improved separation yield adversely affects the energyrequirement.

With the coalescence filter of this invention, in particular whenemployed as coalescence filter for a compressed air stream, a separationyield for contaminant liquid present in the air can be obtained of atleast 40 μg liquid per m³ carrier fluid or carrier gas per 1.0 mbarpressure difference, preferably at least 44 μg, more preferably at least46 μg.

The invention is further elucidated in and by the examples below.

The fibrous materials specified below were tested as coalescence filterfor purifying oil-contaminated air, as described in ISO 12500-1 and ISO8573-2. The initial oil concentration was 10 mg/m³.

Comparative Experiments A-B

A filter material was used comprising the specified number of layers ofa conventional, commercially available oleophobic filter material withproperties as specified in Table 1.

Average Total Wet Maximum pore thickness Air pressure oil Numberdiameter coalescence permeability drop transfer of layers (μm) medium(l/m² · s) (mbar) (mg/m³) Efficiency A 5, 4.7   4 mm 43 283 0.023 92flat layers, oleophilic B 5, 8.2 2.75 mm 109 133 0.12 77.5 flat layers,oleophobic

EXAMPLES 1-2

A coalescence medium was used comprising 14 and 8 layers, respectively,of oleophilic and oleophobic glass fiber material, respectively, havingthe material properties as specified below. The permeability to air wasdetermined according to DIN EN ISO 9237.

TABLE 2 Average Total Wet Maximum pore thickness Air pressure oil Numberdiameter coalescence permeability drop transfer of layers (μm) medium(l/m² · s) (mbar) (mg/m³) Efficiency 1 14, 8.2 7.70 mm 109 212 0.00898.9 flat layers, oleophilic 2 8, 15.9 5.12 mm 210 110 0.203 79.6 flatlayers, oleophobic

From the comparison of Example 1 with Comparative experiment A itappears that the filter efficiency of a thick, open package of filtermaterial is better than that of a thin, closely stacked package. Thepressure drop across the thick open package even appears to be lower.

The comparison of Comparative experiment B with Example 2 shows that thefilter efficiency is similar for a thick, open package and a thin,densely packed package. However, the pressure drop across the thick openpackage is lower than the pressure drop across the thin densely packedpackage

1-21. (canceled)
 22. A coalescence filter for purifying a fluid whichcontains a carrier and at least one liquid contaminant by coalescing ofthe at least one contaminant, wherein the coalescence filter includes aninlet for supplying the fluid to a filter element present in thecoalescence filter, wherein the filter element includes a primarycoalescence medium which is provided for coalescing of the at least onecontaminant in the primary coalescence medium during the displacement ofthe fluid through the primary coalescence medium, wherein thecoalescence filter further includes an outlet for discharging thecoalesced contaminant from the filter element, wherein the primarycoalescence medium comprises at least one layer of a porous material,wherein the primary coalescence medium has a total thickness of at least3.5 mm, preferably at least 4 mm, preferably at least 5 mm, morepreferably at least 6 mm, most preferably at least 7 mm, in particularat least 7.5 mm, measured at a pressure of 2N/cm².
 23. The coalescencefilter according to claim 22, wherein the primary coalescence medium hasa thickness of 50 mm at a maximum, preferably 40 mm at a maximum, morepreferably 30 mm at a maximum, most preferably 25 mm at a maximum, inparticular, 20 mm at a maximum.
 24. The coalescence filter according toclaim 22, wherein the pores in the primary coalescence material have anaverage pore diameter of between 2 and 100 μm, preferably between 3 and70 μm, more preferably between 5 and 50 μm, most preferably between 5and 35 μm, in particular between 5 and 30 μm.
 25. The coalescence filteraccording to claim 22, wherein the primary coalescence medium has an airpermeability of at least 30 l/m².s, preferably at least 50 l/m².s, morepreferably at least 100 l/m².s.
 26. The coalescence filter according toclaim 22, wherein the primary coalescence medium has an air permeabilityof 2000 l/m².s at a maximum, preferably 1750 l/m².s at a maximum. 27.The coalescence filter according to claim 22, wherein the primarycoalescence medium includes a plurality of layers of a same porousmaterial, preferably at least 4 layers, more preferably at least 6layers, most preferably at least 10 layers.
 28. The coalescence filteraccording to claim 22, wherein the primary coalescence medium includesone or more layers of a first coalescence medium and one or more layersof a second coalescence medium, which is different from the firstcoalescence medium.
 29. The coalescence filter according to claim 28,wherein the first coalescence medium is wetting with respect to thecontaminant to be coalesced, and the second coalescence medium isnon-wetting with respect to the contaminant to be coalesced.
 30. Thecoalescence filter according to claim 22, wherein the primarycoalescence medium has a density of between 0.08 and 0.50 g/cm³,preferably between 0.10 and 0.25 g/cm³, more preferably between 0.12 to0.17 g/cm³.
 31. The coalescence filter according to claim 22, whereinthe primary coalescence medium is made of one or more layers of a porousfibrous material, which substantially includes fibers of an averagediameter of 0.25-20 μπl, preferably 0.5-10 μπl.
 32. The coalescencefilter according to claim 22, wherein the coalescence filter includes alayer of a drainage material, preferably adjacent to and along adownstream surface of the primary coalescence medium along whichcoalesced contaminant exits the primary coalescence medium, forreceiving and draining the coalesced contaminant.
 33. The coalescencefilter according to claim 32, wherein the drainage layer is manufacturedof a thermoplastic or thermosetting plastic, an organic or inorganicmaterial, a metallic material or a metal alloy, or a blend of two ormore of said materials and chemically modified forms thereof.
 34. Thecoalescence filter according to claim 22, wherein the coalescence filterincludes a layer of a protective material, adjacent to and along anupstream surface of the primary coalescence medium along which the fluidis supplied to the primary coalescence medium.
 35. The coalescencefilter according to claim 22, wherein the primary coalescence medium ismanufactured from a material chosen from the group of wetting ornon-wetting, hydrophobic, hydrophilic, oleophobic or oleophilic fibrousmaterials or a blend of two or more thereof.
 36. The coalescence filteraccording to claim 22, wherein the primary coalescence medium ismanufactured from an oleophilic or an oleophobic fibrous material or ablend thereof.
 37. A coalescence medium according to claim 22 for use ina coalescence filter according to claim
 22. 38. A method for purifying afluid which contains a carrier and at least one contaminant, wherein thefluid is conducted through a coalescence filter according to claim 22,for reducing the concentration of the at least one contaminant bycoalescing of this contaminant in the coalescence filter.
 39. The methodaccording to claim 38, wherein the fluid is chosen from the group ofcompressed air contaminated with one or more hydrocarbons, contaminatedwater or contaminated hydrocarbons.
 40. The method according to claim38, wherein the at least one contaminant belongs to the group ofliquids, aerosols, macro drops or mixtures of two or more of thesematerials.
 41. The method according to claim 38, wherein the supply offluid to the coalescence filter is continuous.